Over the last several centuries, wind operated pipes have been developed to produce a wide variety of musical sounds. It is customary in pipe organs to provide a separate "set" or "rank" of pipes for each "stop" of the organ. Thus, there might be one rank of sixty-one Diapason pipes (including one pipe for each note), and another rank of sixty-one Flute pipes, and another of sixty-one Trompette pipes, etc. Any particular rank can further be characterized as being made up of "flue" pipes or "reed" pipes. While there are almost countless varieties within each family, flue pipes are all essentially whistles, with the differences in tone color between one flue rank and another being determined by the relative dimensions of corresponding notes, the type of material used in the construction of the pipes, whether the pipes are open or stopped, and other factors.
Reed pipes generate tone in an entirely different manner, in that they employ vibrating brass reeds as the primary source of tone, together with "resonators" for affecting the characteristics of the tone. Over the long period of development of pipe organs, organ reed pipes have been successfully designed to be highly imitative of certain orchestral voices. However, because the natural speech characteristics of a reed, due to its mechanical construction and the operation thereof, are not the same as the speech characteristics of the orchestral instruments they are intended to simulate, it has not been possible to make reeds sound exactly like orchestral voices. Organ reeds none-the-less have a certain quality and charm that cannot be duplicated by orchestral instruments, and it is the object of the present invention to provide an electronic organ that simulates the unique characteristics of reed organ pipes.
A reed organ pipe consists essentially of a reed tube having an opening, called a shallot, cut into one side thereof, against which a brass reed tongue is held by a tuning wire having spring tension, the reed and shallot being enclosed in a boot having an opening at the bottom, which communicates with a windchest to allow air into the pipe when its corresponding valve is operated, and a resonator coupled to the boot. Depending upon the desired organ voice, the resonator takes a variety of forms, such as a tapered, open-ended resonator for a chorus reed stop such as an organ Trompette, a partially closed flared pipe for obtaining an Oboe tone, a slightly tapered pipe with a slot in its wall near its remote end for a more imitative Orchestral Oboe, or capped resonators of various shapes and sizes to achieve other tonal effects. The resonators are usually scaled so as to be approximately one-half the wavelength of the sound of the note to be produced, but many interesting tone qualities are produced by pipes having short length resonators, as for example, the Kinura and Vox Humana.
In operation, the brass reed or tongue vibrates against the shallot, the reed being supported with respect to the shallot so that it essentially "rolls" past the shallot upon opening and closing so as to gradually close the opening; the size and shape of the reed and its curvature relative to the size and shape of the shallot determine the shape of the pulse of air that excites the resonator, which, in turn, determines the tonal quality. The relationship between the reed and the resonator also effect the tonal quality: if the resonator is tuned sharp or flat relative to the tuning reed, the resulting sound is either "choked" or "free", respectively. By appropriately adjusting the shape, configuration and size of the resonator used with a particular reed one can adjust the tone quality of a given pipe over a wide range, making it possible to make organ reed pipes highly imitative of certain orchestral voices. It is again emphasized, however, that the object of the present invention is not to simulate orchestral voices but, rather, to simulate by electronic circuit means the peculiar characteristics of reed pipes, thereby to imitate natural pipe organ voices. It is important that an electronic organ that is intended to imitate a pipe organ, and upon which classical organ literature can be properly interpreted, must be able to imitate both flue and reed pipes. In the interest of economy it is sometimes essential that both types of sound be produced by a common tone generating system. Such attempts however have not been completely successful in that the common origin of the sound has been all too readily apparent. Another important object of this invention. therefore, is to provide means for deriving flue and reed voices simultaneously wherein the reed voices have different speech characteristics as well as different harmonic structures thus to effectively disguise the common origin of the different voices.
It is of course known that the timbre or tonal qualities of the sounds generated by an electronic organ are conventionally achieved by producing an audio frequency signal of the particular waveshape which when reproduced by a loudspeaker produces the desired tonal quality, one common system being characterized as of the "formant" type which starts with a pulse waveshape, for example a rectangular pulse or sawtooth, and uses various filters to attenuate or emphasize desired harmonic frequencies to achieve an audio frequency signal of desired waveshape. For example, Peterson Pat. No. 3,316,341 describes the use of a dynamic filter, a tuned resonant filter that peaks certain frequencies in the audio frequency spectrum and attenuates others, both above and below the frequency to which the filter is tuned, for introducing dynamic variations under player control, in the tone quality of an electrical musical instrument. While the dynamic filter therein described is admirably suited for achieving the sought-after effects, it cannot be used to accurately duplicate or simulate the peculiar speech characteristics of reed organ pipes.